The present invention relates to an optical disk apparatus including an optical head that focus laser light onto an optical disk to record information on the optical disk or reproduce information recorded on the disk.
FIG. 4 shows a semiconductor laser assembled within a package according to a conventional technology as a laser light source. The laser chip 2 of a semiconductor laser 1 is packaged on a base 3 and is sealed by a cap 4 with a glass window. The direction of emission (intensity distribution center) 6 of laser light 5 emitted from the laser chip 2 varies about 3 degrees with respect to the vertical line of the base 3, and the position of the light emission point 26 of the laser chip 2 varies about 80 μm with respect to the center line 35 of the base 3. Further, a light intensity distribution 7 in a plane perpendicular to the direction of emission (center of intensity distribution) 6 of the laser light 5 is symmetric with respect to the direction of emission (center of intensity distribution) 6. The configuration of the package of the semiconductor laser like this is disclosed in, for example, “The Basics and Application of Optical Disk Storage,” published by Electronic Information Communications Institute in 1995, page 48.
FIG. 6 is an example of the configuration of an optical head in the prior art. In a case or housing 8 are arranged a semiconductor laser 1, a beam splitter 9, a collimating lens 10, a cylindrical lens 11, a photodetector 12, and an objective lens 13. The objective lens is supported by the case 8 and configured to be moved by a spring 14.
Laser light 5 emitted from the semiconductor laser 1 passes through the beam splitter 9 and is collimated by the collimating lens 10 and is focused on an optical disk 21 by the objective lens 13.
The optical disk 21 reflects the laser light 5 to the beam splitter 9. The beam splitter 9, in turn, reflects the light 5 to the photodetector 12 via the cylindrical lens 11. A system circuit (not shown) controls the position of the objective lens 13 with respect to the optical disk 21 by the output of the photodetector 12 and reproduces the signal of the optical disk 21.
An optical head having this kind of configuration is disclosed in, for example, “Illustrated Compact Disk Reader (second revised edition)” published by Ohm Co., Ltd., in 1988, page 203. In the configuration shown in FIG. 6, if the direction of emission (center of intensity distribution) 6 of the semiconductor laser 1 is deviated with respect to an optical axis 15 of the objective lens 13 and the collimating lens 10, then the intensity distribution of the laser light 5 reaching the photodetector 12 is deviated, which in turn may cause an offset in the output signal of the photodetector 12, in particular, a track error signal and a focus error signal that utilize a change in the intensity distribution of light in the photodetector 12. For this reason, there is adopted a structure for adjusting the semiconductor laser 1 in such a way that the direction of emission (center of intensity distribution) 6 is aligned to the optical axis 15.
The case 8 is provided with a mounting surface 16 perpendicular to the optical axis 15 of the objective lens 13 and the collimating lens 10. The semiconductor laser 1 is secured to a holder 17 and is secured to the mounting surface 16 in the state in which the direction of emission (center of intensity distribution) 6 is adjusted to be perpendicular to the mounting surface 16 by the use of the holder 17 and a holder base 18. The holder 17 and the holder base 18 are provided with a spherical seat 19 having its center at the laser chip 2, and the holder 17 is bonded and fixed to the holder base 18 in the state in which the direction of emission (center of intensity distribution) 6 is adjusted to be perpendicular to the mounting surface 16 via the spherical seat 19. Further, the holder base 18 gets its position adjusted in the mounting surface 16 in such a way that a laser light emission point 26 is aligned with the optical axis 15 and is secured using screws 20. The configuration described above makes a structure complex and thus difficult to obtain high accuracy even if the holder base 18 and the case 8 are provided with fitting portions. Therefore, it is difficult to make the laser emission point 26 be aligned with the optical axis 15, so it is necessary to make a position adjustment. This kind of configuration of the semiconductor laser and the holder is disclosed in, for example, Japanese Patent Unexamined Publication No. 9-219033.
An exemplary assembling process for the above prior art will be described with reference to FIG. 7. First, the semiconductor laser 1 is pressed into the holder 17 and is fixed there (step 201). The holder is a single, unitary structure according to one embodiment of the present invention. Next, the holder base 18 is fixed to a jig (not shown) and the holder 17 gets its angle adjusted in such a way that the direction of emission of laser light 5 is perpendicular to the mounting surface of the holder base 18, and then the holder 17 is fixed to the holder base 18 (step 202).
Referring now to the main part of the optical head, first, the beam splitter 9 and the cylindrical lens 11 are bonded and fixed to the case 8 (step 211). The case 8 has positioning references for these components and these components are bonded and fixed to the case 8 in accordance with these references. Next, the holder base 18 adjusted in the step 202 is temporarily fixed to the mounting surface 16 of the case 8 (step 212).
Next, the terminal of the semiconductor laser 1 is inserted into the hole of an FPC (Flexible Printed Circuit) (not shown) and is soldered thereto. In a part of the FPC, a drive LSI for driving the semiconductor laser 1 is soldered to a wiring pattern in the previous step, and the drive LSI is connected to a superordinate circuit via a connector. The drive LSI described above makes the semiconductor laser 1 emit light according to a signal from the superordinate circuit. The output terminal of the drive LSI is connected to the terminal of semiconductor laser 1 by a pattern wiring formed on the FPC described above. Further, in the previous step, the photodetector 12 is soldered to the FPC described above (step 213). The output of the photodetector 12 is connected to the superordinate circuit via the connector described above and the laser light described above is used for controlling a position on the optical disk 21 with high accuracy and reproducing information recorded on the optical disk 21.
Next, the collimating lens 10 is mounted on the case 8. The case 8 is provided with a mounting reference surface so as to make the collimating lens 10 move along the optical axis. The semiconductor laser 1 is made to emit light and the position of the collimating lens 10 is adjusted along the optical axial direction to collimate the laser light 5 passing through the collimating lens 10. After an adjustment has been made, the collimating lens 10 is bonded and fixed there (step 214). For example, FIG. 11 shows a cross-sectional view of the collimating lens 10 bounded and secured to the case 8 using a UV-curing adhesive 37. The collimating lens 10 is mounted on a mounting reference surface 47 that is obliquely provided on the case 8.
The parallelism of the laser light 5 emitted from the collimating lens 10 is achieved by detecting the size of an image made when a CCD camera disposed at a sufficient distance away receives the laser light emitted from the collimating lens 10 and by adjusting the position of the collimating lens 10 to make the size of the image not larger than a predetermined size. Next, the position of the holder base 18 is adjusted on the mounting surface 16 to make the laser light emitted from the collimating lens 10 be aligned with the optical axis of the collimating lens 10 and then the holder base 18 is fixed to the mounting surface 16 by the screws 20 (step 215).
Next, an objective lens actuator (not shown) is mounted on the case 8 (step 216). At this time, the objective lens actuator is mounted at a given position on the case 8 by a fitting portion or the like in such a way that the optical axis of the objective lens 13 is aligned with the optical axis of the collimating lens 10. Then, the optical head is mounted on a servo signal adjusting jig to detect the output of the photodetector 12 caused by the laser light 5 which is emitted by the semiconductor laser 1, reflected by the optical disk 21 mounted on the jig described above, and entered into the photodetector 12. The position of the photodetector 12 is adjusted in such a way that a focus signal and a tack error signal, which are produced by the output of the photodetector 12 described above, satisfy predetermined characteristics, and the photodetector 12 is bonded and fixed there (step 217). The above-mentioned steps constitute the assembling process of the optical head according to a conventional technology.